I’ll let an Orthodox explain their position, but I would add that it is not necessary that Mary be Immaculate - Latin Catholics don’t “need” this doctrine either.
Some people are of the mistaken belief that the only way Jesus could have been sinless is if Mary is sinless. The flaw in that reasoning is that if God could have prevented Mary from inheriting original sin, he could do likewise for Jesus.
If the only way a person can be born without original sin is for the parent(s) to not have original sin then Mary’s parents would need to be free from original sin, and all of her other ancestors as well.
